TABLE 3-1 Microbial Agents of Known Hazard Via Water Exposures
|• Adenoviruses||Conjunctivitis, gastroenteritis, respiratory disease, pharyngoconjunctival fever|
|• Coxsackieviruses||Meningitis, pharyngitis, conjunctivitis, encephalitis|
|• Echoviruses||Gastroenteritis, encephalitis, meningitis|
|• Hepatitis A virus||Hepatitis|
|• E. coli O157||Hemorrhagic diarrhea|
|• Campylobacter jejuni||Campylobacteriosis|
|• Vibrio||Gastroenteritis, wound infection|
NOTE: These agents are known to be present in treated wastewaters or surface water and therefore are considered to be potentially present in waters used for the production of reclaimed water.
SOURCE: Asano et al. (2007).
The occurrence and concentrations of microbial pathogens in reclaimed water depend on the health of the tributary population and the applied wastewater treatment processes (see Table 3-2). Primary and secondary treatment (see Chapter 4) attenuate microbial pathogens but do not eliminate them. For pathogenic bacteria, viruses, and protozoa that can cause acute diseases with even a single exposure, additional physiochemical treatment processes (discussed in Chapter 4) may be required to achieve acceptable levels of removal or inactivation, depending on the beneficial use.
Often known as parasitic worms, helminths pose significant health problems in developing countries where wastewater reuse is practiced in agriculture using raw sewage or primary effluents (Shuval et al., 1986). The World Health Organization (WHO) has pointed to the need to study the transmission of intestinal parasites, particularly nematodes, in children living in areas where untreated wastewater is used for vegetable irrigation (WHO, 1989). Human exposures to helminths are mainly through ingestion of helminth eggs in food or water contaminated with untreated wastewater or sewage-derived sludge, and these exposures can cause acute gastrointestinal illness. There are over 100 different types of helminths that can be present in sewage, although the number of helminth eggs in untreated wastewater is typically much higher in developing countries than in developed countries. The concentration of helminth eggs can range from <1 to >1,000 per 0.3 gallon (1.0 L) of sewage, depending on the source of sewage (Jiménez, 2007; Ben Ayed et al., 2009). Helminth eggs can be largely removed through
TABLE 3-2 Reported Ranges of Reclaimed Water Quality for Key Water Quality Parameters After Different Degrees of Treatment
|Constituent||Units||Untreated Wastewater||Range of Effluent Quality After Indicated Treatment|
|Conventional Activated Sludge (CAS)||CAS with Filtration||CAS with Biological Nutrient Removal (BNR)||CAS with BNR and Filtration||Membrane Bioreactor (MBR)|
|Total suspended solids (TSS)||mg/L||120-400||5-25||2-8||5-20||1-4||<2|
|Total organic carbon (TOC)||mg-C/L||80-260||10-40||8-30||8-20||1-5||0.5-5|
|Volatile organic compounds (VOCs)||μg/L||<100->400||10-40||10-40||10-20||10-20||10-20|
|Total coliforms||No./100 mL||106-109||104-105||103-105||104-105||104-105||<100|
|Protozoan cysts and oocysts||No./100 mL||10-104||10-102||0-10||0-10||0-1||0-1|
NOTE: None of the treatments in the table include disinfection.
aWith anoxic zone.
SOURCE: Asano et al. (2007).